Incandescent electric lamp



Jan. 25, 1938.

c. H. BRASELTON INCANDESCENT ELECTRIC LAMP Filed Aug. 25

INVENTOR Patented Jan. 25, 1938 UNITED STATES INCANDESCENT ELECTRIC LAMP Chester H. Braselton,

New York, N. Y., assignor to Sirian Lamp Company, Newark, N. J., a corporation of Delaware Application August 25,

2 Claims.

This invention relates to incandescent electric lamps and particularly-to a light emitting filament therefor.

Where a tantalum filament is used in an electric lamp it has the tendency to absorb gases from the interior of the bulb at comparatively low temperatures. The effect of the absorption of gases on the tantalum raises its resistance, and therefore less current will flow through the wire and the wire will not be raised to as high a temperature as originally intended. Thus the longer a tantalum lamp is burned the more gases are absorbed by the filament, and the resistance gradually increases and the light emission from the filament becomes lower and lower. The rate of absorption, however, is much lower when the tantalum is maintained at relatively high temperatures, and. it is therefore one of the objects of the present invention to maintain a tantalum filament at a high temperature regardless of its absorption of gases so that the rate of absorption will be relatively low and the light emission will be maintained at a constant high figure.

Another object of the invention is to increase the mechanical strength of a lamp filament at high temperatures.

Other objects of the invention will be apparent as the description thereof proceeds.

One embodiment of the invention has been illustrated in the accompanying drawing in which:

Fig. l is a side elevational view of anelectric lamp embodying the particular type of filament;

and

Fig. 2 is an enlarged view partly in section of the filament used.

In Fig. 1 of the drawing an incandescent electric lamp is shown having the usual form with 40 an envelope ID of glass or other suitable transparent material provided with an inturned press H which has fused to it at approximately the center thereof an upstanding glassrod l2 which extends upwardly to a point adjacent the largest A pair of support rods M are sealed in the press II and have lead-in wires l5 connected to the lower ends thereof. The lighting filament I6 is attached to the upper ends of the support rods l4 and extends in a circular curve around the button I3, there being a plurality of support wires l'l sealed in the button l3 and provided with pig-tails I 8 at their ends to support the filament in its proper position.

The filament itself is preferably formed of a part of the bulb and terminates in a button l3.

1932, Serial No. 630,380 (Cl. 176-40) plurality of wires twisted together, one of the wires being tantalum and the other being a wire having a higher melting point than tantalum. For purposes of illustration I have shown in Fig. 2 a tantalum wire l9 twisted together with a 5 tungsten wire 20 and the twisted filament thus formed wound in a concentrated coil illustrated by the turns 2| at the right hand side of the figure.

When current is run through the filament 10 the temperature of the entire filament is maintained slightly higher than the temperature would be if the filament were made of tantalum only, and thus the tantalum in the filament is prevented from absorbing gases and its resistance is maintained at a constant figure. If, however, the tantalum does absorb some gases and thereby attains a higher resistance, more current will flow through the tungsten wire with the result that its temperature will be raised slightly and the temperature of the tantalum will thereby be increased due to its physical contact with tungsten. The filament of the invention, therefore, has the advantages of a tantalum filament with the disadvantages thereof largely eliminated.

While a single wire each of tantalum and tungsten may be found preferable the invention also contemplates the use of a larger number of wires either twisted together or braided, and these wires may be equally divided between tantalum and tungsten or there may be one tungsten wire with several tantalum wires or vice versa. The tightness of the coiling or braiding may also be varied considerably as a loosely wound coil or braid may be made to accomplish the desired result, it being only necessary to have the tantalum within the high temperature zone of the tungsten to maintain the temperature of the tantalum at a point slightly higher than its normal temperature for the current consumed.

Other modifications of the invention may be resorted to without departing from the spirit thereof and I do not, therefore, desire to limit myself to what has been shown and described except as such limitations occur in the appended claims.

What I claim is:

1. An incandescent electric lamp comprising a globe having electric circuit leads, a filament of tantalum electrically connected at opposite ends directly with said leads, and means for heating said tantalum filament to temperatures in excess of its normal lighting temperature com" prising a tungsten filament electrically connect- 5 ed at its opposite ends with said leads in complete electrical parallelism with said tantalum filament and in contact therewith throughout its length, the cross-section of the tantalum and tungsten filaments being substantially equal.

2. An incandescent electric lamp comprising a globe having electric circuit leads, a filament of tantalum electrically connected at opposite ends directly with said leads, and means for heating said tantalum filament to temperatures in excess of its normal lighting temperature comprising a tungsten filament electrically connected at its opposite ends with said leads in complete electrical parallelism with said tantalum filament and in contact therewith throughout its length.

CHESTER, H. BRASELTON. 

